A semiconductive compound such as gallium arsenide is used in lasers, solar cells and solid-state circuit components such as transistors. In many instances it is necessary to provide a substrate of such a compound with an insulating oxide layer, e.g. in integrated structures of the MOS (metal-oxide-semiconductor) type or as an encapsulant of the substrate during ion implantation and subsequent thermal activation.
Gallium arsenide, in particular, can be directly oxidized only at high temperatures at which decomposition of the compound may become a problem. Other conventional techniques, such as anodic oxidation in a liquid electrolyte or in a gas plasma, are ineffective with semiconductors because of their high electrical resistivity. Thus, the practice has been to provide substances of gallium arsenide with insulating layers of unrelated oxides; this procedure is rather inconvenient and not very reliable since it gives rise to stresses at the semiconductor/oxide interface which in turn result in poor adhesion.